Anyone know the breed of Betty?

This little chicken was thrown over an 8 foot wall into my friends yard along with her 3 RSL pullet friends. She lives in inner city Liverpool, not the usual place where people normally dump chickens! They are all healthy and out of the 4 of them I am getting 2 smallish brown eggs a day. I am not sure who the eggs are from, could be Betty but then maybe not. I presume they are only small because the pullets are only young, is that correct? Anyway I am digressing. Does anybody know if Betty is a particular breed or is she a mutt chicken? She is only small, maybe a bit larger than half of the size of her RSL friends.

Her ear lobes are red. What is a Birchen? I have had a look on the internet and it only seems to be in tandem with another breed such as 'Birchen Cochin' or 'Birchen Marans', I can find any that look like her. Thank you for replying so quickly!